Currently, the most common process for heavy oil up-gradation is the Delayed coking process. A Delayed coker operates on the principle of thermal cracking and produces solid coke, gaseous and liquid products from heavy hydrocarbon feedstock. During the coking process, heavy hydrocarbon feedstock are heated in a furnace, passed through a transfer line and discharged into a coking drum. The feedstock is thermally converted to solid coke and vapors. The vapors formed in the coke drum leave the top of the drum and are passed to a fractionating column where they are separated into liquid and gaseous products. Sometimes these products are recycled with residual feed to the coke drum.
Worldwide, the deteriorating crude quality has resulted in higher yields of heavy residue with high Conradson carbon and higher sulphur and metals, which has in turn resulted in higher coke yield while processed in Delayed coker. The fuel grade pet coke produced from this heavy residue with high Conradson carbon and higher sulphur has lower price resulting in reduced margin around Delayed coker. Recently, technology improvements has focused on reducing cycle times, recycle rates and drum pressure with or without increase in heater outlet temperature to reduce coke yield and increase valuable gas and liquid yield. In the present scenario, the major aim of the refiner's is to minimize coke production and maximize gas and liquid products from residual feedstock.
Any process improvement in Delayed coking process which reduces the coke production and increases the liquid production is of interest to refiners. One of the processes used to improve Delayed coker operation is disclosed in U.S. Pat. No. 3,493,489 (U.S Class 208-50), which describes a process of integration of Fluid catalytic cracking and Delayed coking process which means that coker feed material can include the bottoms from the catalytic cracker fractionator column which includes decanted or slurry oil material.
U.S. Pat. No. 3,891,538 discloses the use of decanted oil, comprising the material boiling above 425° C. which is passed into coking zone along with residual feedstock.
U.S. 2011/0232164 A1 discloses a process of co-processing biomass pyrolysis oil along with heavy residues into the coking process to improve the operation of Delayed coking process and to utilize the biomaterial for the production of transportation fuels. However, this patent does not indicate any reduction of coke yield and enhancement of gas and liquid yields.
WO 2010/012997 A2 describes a process for production of biooil in Delayed coker unit by Co-feeding of biomass together with the conventional fresh feed of residual hydrocarbon feedstocks. However, this patent does not provide any information on the reduction in coke yield and increase in gas and liquid yield.
The object of the present invention is to provide an improved Delayed coking process in which feedstock to the coking zone is a mixture of residual heavy hydrocarbon feedstock and biooil which increase the liquid products produced from the coking zone and decreases the amount of solid coke produced in the coking zone.
The present invention overcomes one of the main problems associated with commercially operated Delayed coking processes. The primary object of these commercial processes is to produce high value low boiling liquid products from low value residual heavy hydrocarbon feedstock which normally boil in the range of from about 450° C. to 700° C. However, during the production of high value lighter liquid products, low value solid coke is also produced. This solid coke presents problems in handling and competes with other low cost solid fuels like coal. Accordingly, refiners attempt to reduce the amount of solid coke produced in Delayed coking process while attempting to increase the valuable C5+ liquid components produced.